New imaging technologies are revealing ever greater details of motor behavior in the fetus for clinical diagnosis and treatment. Understanding the form, mechanisms and significance of fetal behavior will be important for maximizing clinical application of imaging tools. Our long-term objectives are to determine if fetal movements and the environment in which they are generated contribute to adaptive postnatal motor behavior. Results of our studies will provide fundamental information relevant to questions of environmental impact on the neural control of prenatal limb movements during normal development in utero and when environmental forces are altered by extremely premature birth. The chick embryo, like the fetus, begins generating complex movements such as kicking and stepping early in development, and is a valuable model of fetal behavior because it is amendable to experimental study throughout embryonic development. We propose to advance our long-term objectives by studying a distinct array of repetitive leg movements that emerge in the final days of embryonic development preceding onset of hatching and bipedal locomotion. We will record synchronized kinematics and electromyography (EMG) to capture spontaneous leg movements within the egg for several hours continuously between embryonic days 15 and 22. Our pilot data suggest that there is more than 1 muscle pattern and an array of frequencies (2-10 Hz) associated with these movements. In Specific Aim 1 we will determine the array of EMG and kinematic patterns for these leg movements and the developmental course for each pattern. The repetitive movements emerge just as muscle spindles are established, but it is not known if muscle afferent information impacts movement pattern selection prenatally. So in Specific Aim 2 we will determine if EMG and kinematic patterns during repetitive leg movement are altered by mechanical perturbations that alter available movement space or limb posture one or more days prior to hatching. It is also not known if prenatal limb movement experience is critical for development of coordinated limb action postnatally. Thus in Specific Aim 3 we will determine if the age at onset and the rate of maturation for these leg movements is shifted in time when the time to hatch and begin walking is accelerated or delayed. We will accelerate the time to hatch by incubating eggs in constant light and delay time to hatch by incubating eggs in constant dark. [unreadable] [unreadable] [unreadable]